Apparatus for continuous etching and anodizing of aluminum

ABSTRACT

Elongated aluminum bodies such as aluminum sheets, foils and the like, the term aluminum denoting not only pure aluminum but also aluminum alloys which lend themselves to electrolytic etching and anodizing, are continuously passed through two electrolytic cells to be etched in the first and anodized in the second cell, at least one of the two cells comprises two adjacent compartments each equipped with a stationary electrode and containing electrolyte. The other cell may be similarly constructed or may be a single compartment electrolytic cell including electrolyte and a stationary electrode wherein the elongated aluminum body passing therethrough forms the electrode of opposite polarity. Alternating current is applied to the double compartment cell and, if one of the electrolytic cells is of the single compartment type, direct current is applied thereto. The elongated aluminum body forms during its passage through the double compartment cell a bipolar conductor having portions within the respective compartments of this cell. It is possible in this manner, i.e., by utilizing two cells at least one of which being a two-compartment cell, to carry out etching and anodizing in a single continuous pass of the elongated aluminum body.

errtinri et at.

[ APPARATUS FUR CGNTJlNIUGUS ETCHTNG AND ANUDIZIING 011 ALUMINUM [75] Inventors: iileut Friedrich iilerrrnann;

Roionoio M. illizon, both of Cologne, Germany [73] Assignee: Metailoxyd Gesellseiintt rnit iiesehrnnirter lliiaitung, Kolnbraunsfeld, Germany Notice: The portion of the term of this patent subsequent to Apr. 25, 1989, has been disclaimed.

[22] Filed: .lluly 12, 19711 [21] Appl. No.: 161,789

Related US. Application Data [62] Division of Ser. No. 762,806, Sept. 26, 1968, Pat.

[30] Foreign Appiication Priority Data Oct. 17, 1967 Germany P 16 21 115.7

[52] 111.8. 113i 204M207, 204/28, 204/33, 204/206, 204/208 [51] lint. Cl (3221b 5/68 [58] Field oi Search 204/28, 33, 58, 206, 204/207, 208, 211

[5 6] Reterenees Cited UNITED STATES PATENTS 2,755,238 7/1956 Turner 204/33 3,296,114 1/1967 Lloyd 204/206 2,541,275 2/1951 Odier 204/28 2,901,412 8/1959 Mostovych et al. 204/58 3,471,375 10/1969 Cooke et a1. 204/206 *Get. 116, i973 FOREIGN PATENTS OR APPLlCATlONS 926,385 5/1963 Great Britain 204/206 237,178 5/1959 Australia 204/28 Primary Examiner-John H. Mack Assistant Examiner-W. 1. Solomon AttorneyMichael S. Striker [5 7] AlBSTlltAtIT Elongated aluminum bodies such as aluminum sheets, foils and the like, the term aluminum denoting not only pure aluminum but also aluminum alloys which lend themselves to electrolytic etching and anodizing, are continuously passed through two electrolytic cells to be etched in the first and anodized in the second cell, at least one of the two cells comprises two adjacent compartments each equipped with a stationary electrode and containing electrolyte. The other cell may be similarly constructed or may be a single compartment electrolytic cell including electrolyte and a stationary electrode wherein the elongated aluminum body passing therethrough forms the electrode of opposite polarity. Alternating current is applied to the double compartment cell and, if one of the electrolytic cells is of the single compartment type, direct current is applied thereto. The elongated aluminum body forms during its passage through the double compartment cell a bipolar conductor having portions within the respective compartments of this cell. It is possible in this manner, i.e., by utilizing two cells at least one of which being a two-compartment cell, to carry out etching and anodizing in a single continuous pass of the elongated aluminum body.

10 Cllailms, 3 Drawing 1F igures Patented 0d. E6, 1973 v 3,756,043.

INVE TOR$ HELMUT F/P/EDP/(l/ l/EAI? ANN Y Mam/M m. Maw

APPARATUS lFOlit CONTINUOUS ETCll-llllNG AND ANOUIZIING UHF ALUMINUM CROSS REFERENCE TO RELATED APPLICATION This is a Divisional application of the parent application Ser. No. 762,806, filed Sept. 26, 1968, and entitled Method And Apparatus For Continuous Etching And Anodizing Of Aluminum now U.S. Pat. No. 3,632,486.

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for the electrolytic etching (roughening) and electrolytic oxidation of elongated aluminum bodies such as aluminum foils, bands or sheets. The term aluminum is meant to denote not only pure or technically pure aluminum, but also aluminum alloys which lend themselves to electrolytic etching and anodization.

Etched or roughened foils or strips of aluminum are well known and used for many industrial purposes. The etching of the surface of the foils or strips may serve for technical or decorative purposes. Such decorative purposes included the roughening of the surface of aluminum wall coverings and the like. Industrial and technical purposes are served by the roughening of aluminum foils or strips which are to be used as printing foils or which are to be coated or covered with pigments.

Apparatus for roughening of aluminum surfaces by mechanical treatment, chemical etching or electrochemical methods also is well known. According to the conventional electrochemical apparatus for the purpose of roughening an aluminum surface, primarily electrolytic apparatus are utilized in which the aluminum body which is to be treated serves as electrode in an acid bath which is in contact with a further electrode. Depending on the other process conditions, generally the electrolytic roughening requires a period of the magnitude of several minutes.

Apparatus for electrolytic oxidation of etched or roughened aluminum surfaces, particularly in order to harden such surfaces and to make them chemically resistant, also has been proposed. In accordance with the apparatus, the roughened aluminum body which is to be electrolytically oxidized is introduced as one of the electrodes into an acid bath including an electrode of opposite polarity, i.e., an electrolytic cell is formed in which the aluminum body represents the anode.

Since according to the above-mentioned apparatus for the electrolytic etching or roughening of aluminum bodies, as well as for the electrolytic oxidation, the aluminum body serves as one of the electrodes in an acid electrolyte, it was not possible up to now to carry out electrolytic etching and electrolytic oxidation in a continuous manner, i.e., so that the aluminum foil, strip, sheet or the like would pass as a continuous strip sequentially through the electrolytic etching and the electrolytic oxidizing device. By proceeding in this manner, it would have been unavoidable that short circiuts from one cell to the other were caused by the connecting aluminum strip. Consequently, it was necessary to carry out the two electrolytic processes separated from each other, thereby requiring relatively large expenditures for equipment, operational personnel and also long periods of time for completing the two processes.

Alternating current operated electrolytic cells are known which comprise two chambers or compartments adjacent each other, each equipped with a stationary electrode and containing electrolyte. Alternating current is applied to the electrodes respectively located in the two chambers, and the aluminum strip or the like passing from one of the chambers to the other forms a bipolar conductor therebetween.

It is also known to clean electrochemically etched aluminum surfaces by brushing and rinsing, or chemically by immersion in a bath of dilute aqueous sodium hydroxide solution.

It is an object of the present invention to provide an apparatus for the etching and anodizing of aluminum which will permit to carry out the etching and anodizing of strips and the like in a single continuous process, whereby a continuous strip passes sequentially through an electrolytic etching cell and therefrom through an electrolytic oxidizing cell. lBy proceeding in this manner, i.e., in accordance with the present invention, substantial savings on equipment, space, operating personnel and process time are achieved and a product of highly uniform and desired quality is obtained.

SUMMARY OF THE INVENTION The present invention thus proposes an apparatus for implementing a process for continuously and sequentially etching and anodizing aluminum sheets, foils and the like, according to which such sheets, foils or strips of aluminum or aluminum alloy which may be electrolytically etched and anodized are passed through two sequentially arranged electrolytic devices each connected to a source of electric current, so as to subject the strip in the first of the electrolytic devices to etching and in the second of the electrolytic devices to an odic oxidation. At least one of the two electrolytic devices comprises two adjacent compartments, each equipped with a stationary electrode and containing electrolyte. Alternating current is applied to the stationary electrodes in the two compartments and the strip forms during its passage through the compartments a bipolar conductor having portions within the respective compartments of the device. The other of the two electrolytic devices may be of similar structure, or may be an electrolytic single chamber cell including electrolyte and a stationary electrode, wherein then the strip passing therethrough will form the electrode of a polarity opposite to that of the stationary electrode.

The first of the two devices will serve for etching and the second for anodizing the strip. The electrolyte of the etching cell preferably will consist of dilute hydrochloric or hydrofluoric acid, whereas the electrolyte of the anodizing cell preferably will consist of dilute sulfuric acid. The external ohmic resistance between the sources of alternating current (if two of the two-compartment cells are used) should be such that no significant amount of current will flow in an external conduit between the two sources of current, and no significant amount of current should flow within the portion of the aluminum or the like strip located between the two electrolyticdevices.

The same conditions with respect to ohmic resistance will also apply in cases where only one of the two elec trolytic devices is of the two-compartment type described above and the other is of the above-described single chamber structure.

Preferably, the source of electric current for the two electrolytic devices will be independent from each other. Cleaning baths, rinsing and drying devices may be interposed along the path of the aluminum strip between the first and second electrolytic devices, i.e., between the etching and anodizing of the strip, and the anodized strip may be rinsed and sealed after leaving the anodizing electrolytic device.

The novel features which are considered as characteristic fo the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a schematic illustration of an apparatus according to the present invention in which both electrolytic devices are of the two-chamber alternating current type;

FIG. 2 illustrates schematically an apparatus according to the present invention according to which the etching is carried out in a two chamber alternating current electrolytic device and the anodizing is carried out in a direct current-operated single cell electrolytic device; and

FIG. 3 is a schematic illustration of an apparatus according to which the etching is carried out in a direct current, single cell electrolytic device and the oxidizing is carried out in an alternating current two chamber electrolytic device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, the continuous, sequential etching and anodizing of the aluminum strip or the like is carried out by first electrolytically etching and thereeafter electrolytically oxidizing the continuous moving strip whereby at least one of these two electrolytic processes is carried out in an electrolytic device which comprises at lease two chambers each equipped with one electrode, whereby the electrodes are connected to a source of alternating current. The strip passing sequentially through the two chambers of this electrolytic device forms during passage from one to the other of the two chambers a bipolar conductor.

Thus, it is essential according to the present invention to utilize for the etching and/or oxidation of the aluminum strip or the like a two-chamber, alternating current electrolytic cell in which the foil or strip which is to be treated, i.e., which is to be etched or oxidized does not form one of the electrodes but only a bipolar conductor whereby it is achieved that electric shunts between the abovedescribed electrolytic device and the other of the two electrolytic devices will be avoided.

Thus, at least one of the two electrolytic devices must be of the above-described two chamber type, whereas the other of the two electrolytic devices may be of the same type or may be a direct current electrolytic cell in which the aluminum strip passing therethrough forms one of the two electrodes.

It is thus possible, in accordance with the present invention, to carry out electrolytic etching as well as electrolytic oxidation successively on one and the same continuous strip and the like which passes in the indicated sequence through the two electrolytic devices. It has been found that proceeding in accordance with the present invention does not only substantially reduce the total time requirement for etching and anodizing due to the fact that the etching and anodizing may now be carried out in a continuous manner, but furthermore, that the entire surface treatment can be carried out in a period of less than one minute and will result in aluminum or the like surfaces of very high quality. The total surface treatment, i.e., the etching as well as the anodizing, is carried out, in accordance with the present invention, in a substantially automatic manner which also simplifies the control of the process and particularly of the treating baths.

According to one embodiment of the present invention, electrolytic etching as well as electrolytic oxidation is carried out in the double or multi-chamber electrolytic devices described above each of which comprises at least two chambers, each equipped with a single stationary electrode and work, such as an aluminum strip or the like extending through both chambers forming a bipolar conductor but not one of the electrodes thereof.

According to another embodiment of the present invention, the electrolytic etching is carried out in a direct current electrolytic device in which the aluminum foil, strip or the like forms the cathode, and the electrolytic oxidation is carried out in a multichamber, alternating current electrolytic device as described above.

However, this sequence may also be reversed, and thus, according to still another embodiment of the present invention, the electrolytic etching is carried out in the multi-chamber, alternating current electrolytic device whereas the electrolytic oxidation is carried out in a direct current cell in which the foil or strip acts as the anode.

It is also within the scope of the present invention to cleanse the foil or strip after the electrolytic etching and prior to the electrolytic oxidation in a, per se, known manner, for instance by passage through a bath of dilute aqueous sodium hydroxide.

It is also possible and within the scope of the present invention to subject the foil or strip during the continuous etching and anodizing process to coloration. The sealing of the roughened and electrolytically oxidized aluminum surfaces in boiling, de-ionized water may also be combined with the above-described steps of the process of the present invention. All of these additional treating steps such as cleansing, coloring and sealing may be incorporated into the single continuous pass of the aluminum strip, foil or the like and thus are carried out in a particularly simple, economical and quick manner.

The roughened or etched surface obtained by the method of the present invention appears to be of better quality than that obtained by conventional methods. For certain technical purposes, particularly the utilization of the aluminum or aluminum foil or strip as printing foil or plate, it has been found advantageous to carry out the etching so as to achieve a surface roughness of between 2 and 3 microns, which may be accomplished by subjecting the strip, foil or the like to electrolytic etching at a current density of 20 amperes per square centimeters and for a period of between 0.5 and 0.75 minutes.

If a surface roughness of only between 1 and 2 microns is desired, preferably a current density of about 16 amperes per 100 square centimeters will be applied for a period of between 0.5 and 0.75 minutes.

According to one embodiment of the present invention, the arrangement for carrying out the abovedescribed process will comprise an electrolytic etching device represented by a two-chamber, alternating current electrolytic cell in which the aluminum strip or the like forms a bipolar conductor but is not used as one of the electrodes, and which contains for instance a dilute aqueous hydrochloric acid as electrolyte in both of the chambers. The device will include suitable rollers or the like for guiding the foil or band sequentially through the two chambers. The foil or strip leaving the second or last of the chambers of the etching device passes through a more or less conventional rinsing bath or the like and then into a second two-chamber, alternating current electrolytic device of the type described above in which, however, the electrolyte is dilute aqueous sulfuric acid and which also is equipped with suitable guide means for passing the foil or strip sequentially through the two chambers of this second or anodizing cell.

According to another embodiment of the present invention, the etching is carried out in a direct current electrolytic cell in which the minus terminal of the source of direct current is in contact with a guide roller for the foil or strip so that the foil or strip while passing through this cell will become the negative electrode. The cell contains dilute aqueous hydrofluoric acid as electrolyte and is equipped with a stationary electrode connected to the positive terminal of the source of direct current. Again, suitable devices for the guiding of the strip through the direct current etching cell are provided and the etched strip passes through a rinsing bath or the like into an anodizing device which, in this case, must be a twoor multi-chamber alternating current electrolytic cell of the type described further above and holding in both chambers dilute aqueous sulfuric acid as the electrolyte. Again, suitable arrangements are made for guiding the foil or strip sequentially through the two chambers of the anodizing device.

According to yet another embodiment of the present invention, the etching device is a two-chamber alternating current electrolytic cell of the type described above, holding dilute aqueous hydrochloric acid as the electrolyte and provided with suitable arrangements for guiding the foil or strip sequentially through the two chambers of the electrolytic device and again the strip does not form one of the electrodes but is in the nature of a bipolar conductor passing through the two chambers of the cell. The thus-etched strip is then passed through a rinsing device and from there into a direct current, single-cell electrolytic device holding dilute sulfuric acid as the electrolyte and provided with guide means for passing the strip through the cell. In this case, the guide means preferably include a conductive roller connected to the positive terminal of a source of direct current so that the strip upon contact with this roller will become the positive electrode of the direct current electrolytic cell which is also provided with a negative electrode connected to the negative terminal of the source of direct current.

Preferably, in all of these embodiments of the present invention, a bath holding dilute aqueous sodium hydroxide is interposed between the etching and the anodizing device, again equipped with suitable guide means for passing the etched strip therethrough, and this bath will serve for cleansing of the etched foil prior to anodizing of the same.

It is also within the scope of the present invention to include in the continuous process of etching and anodizing and in the arrangement for carrying out this process, a rinsing and sealing device through which the anodized strip is passed and whereby the sealing device may be a bath of boiling de-ionized water.

The following examples are given as illustrative only without, however, limiting the invention to the specific details of the examples.

In the examples, reference will be made to the Figures of the drawing in which identical elements are identified by identical reference numerals.

EXAMPLE 1 The present invention is described in the present example with reference to FIG. 1 of the drawing as utilizing two double chamber alternating current electrolytic devices. Aluminum strip 112 is fed from coil it into the alternating current, two-chamber electrolytic device M.

Electrolytic device or cell 1141- comprises two chambers lb and 18 separated from each other by wall 17. Each of the chambers contains dilute aqueous hydrochloric acid. Each of the chambers lid and i7 is equipped with one electrode, 32 and 34 respectively, which electrodes are connected to a source of alternating current identified by reference numeral 36. Coil or strip 12 passes over guide roller 241 into first chamber 16 in the bottom portion of which a further guide roller 26 is arranged. Another guide roller 2b is arranged substantially above separating wall 117 so that the strip will pass through the electrolyte of chamber lib, then out of the same over guide roller 2ft into the electrolyte of chamber lid. In second chamber 13 a further guide roller 2% is arranged near the bottom thereof and the aluminum strip is guided thereby through chamber w and from there by guide roller 3t) out of the electrolytic, alternating current etching device. it will be noted that strip 112 does not form one of the electrodes and thus may be called, particularly in the vicinity of guide roller Ztl, i.e., between chambers in and iii, a bi-polar conductor.

The thus-etched strip is passed from guide roller 3% through a rinsing device 3% in which electrolyte adhering to the strip is removed. From there, strip 12 passes, suitably guided by rollers d2, through a cleansing device dtl which is represented by a container holding dilute aqueous sodium hydroxide.

Electrolytic two-chamber cell M, as well as cleansing device 40, are provided with suitable, per se conventional, heating arrangements which, for sake of clarity, have been omitted in the drawing.

From cleansing container 40, the strip i2 is passed through a second rinsing device 35% and from there through a conventional heating device for the purpose of being dried.

The thus-etched, cleansed and dried strip is then passed through an electrolytic oxidation device 4 8, represented by a second two-chamber, alternating current electrolytic cell which again comprises two chambers 5t]! and 52 separated from each other by wall M. The electrolyte in chambers MD and 52 consists of dilute aqueous sulfuric acid. Each of chambers 5t) and 2 is equipped with one electrode, 5d and M: respectively, and electrodes b t and 5b are connected to a source of alternating current identified by reference numeral $8. Somewhat different from the etching cell M, the strip is passed from chamber 50 to chamber 52 through a suitable opening in wall 51, for instance through a rubber gasket arranged in wall 51 so as to permit passage of the strip therethrough without causing intermingling of the electrolyte of the two chambers.

The arrangement used according to electrolytic cell 14 for the passage of the strip from the first to the second chamber is practical only if the strip is of sufficient flexibility, whereas the arrangement utilized in electrolytic cell 48 will permit the treatment of a strip of greater stiffness since the strip need not be bent while passing from chamber 51 to chamber 52.

Thus, in any specific given case, it will have to be decided, depending on the mechanical characteristics of the strip whether the arrangement of cell 14 or the arrangement of cell 48 is best suitable for the passage of the strip from the first to the second chamber of the respective electrolytic device.

After leaving electrolytic device 48, the thusanodized strip is passed through another rinsing device 38 to a conventional drying device 46 and the thusdried, etched and anodized strip 12 may then be wound to form a coil 68.

When it is desired to subject the anodized strip to sealing, it is proposed to interpose a container 62 between last rinsing device 38 and last heating and drying device 46, through which the strip is passed by suitable guide rollers 64, in which sealing of the oxide layer is accomplished by contact with boiling de-ionized water.

The method of the present invention may be carried out in the above-described device, for instance by utilizing as electrolyte in the chambers 16 and 18 of etching cell 14 dilute aqueous hydrochloric acid having a concentration of 1.5 percent by volume. The temperature of the dilute hydrochloric acid preferably will be maintained between 20 and 80C and most preferably at about 50C C.

The source of alternating current has a voltage of between 30 and 60 volts and a current density of between 5 and 25 amperes per 100 square centimeters is maintained. The strip is passed through the etching cell at such speed as to obtain a treating time of between 30 and 45 seconds.

The second electrolytic two-chamber device 48 contains as electrolyte dilute aqueous sulfuric acid having a concentration of percent by volume and being maintained at a temperature of between about 30 and 50C. Anodizing is carried out at a current density of between 10 and 30 amperes per 100 square centimeters.

It would be possible, of course, to carry out in the context of the present invention the cleansing of the etched strip by conventional brushing of the same, but it is preferred to carry out chemical cleansing in container 40 by passing the strip therein through dilute aqueous sodium hydroxide having a concentration of within the above range are excellently suitable for producing printing plates thereof.

A lesser degree of surface roughness, such as between about 1 and 2 microns, which generally suffices if the strip or foil is to be used for decorative purposes, is obtained by reducing under otherwise equal conditions the current density to about 16 amperes per 100 square centimeters.

EXAMPLE 2 Another embodiment of the present invention will be described in the present example with reference to FIG. 2 of the drawing in which for sake of simplicity the arrangements for cleansing and sealing have been omitted, although cleansing and sealing arrangements may be included in the overall arrangement schematically illustrated in FIG. 2 at the points thereof corresponding to the points at which these arrangements appear in FIG. 1.

The process and arrangement according to FIG. 2 differs from that described in connection with FIG. ll particularly by utilzing as oxidizing electrolytic cell a direct current electrolytic device. The strip is passed through an etching device and ancillary devices corresponding to those of FIG. 1 until it reaches guide roller 74 which is connected to the positive terminal of a source of direct current. From guide roller 74, the strip passes through the electrolyte of electrolytic cell 70 which consists of dilute sulfuric acid. For this purpose, three further guide rollers are indicated. A negative electrode 78 connected to the source of direct current is immersed in the electrolyte.

The direct current anodizing device 70 may contain as electrolyte dilute sulfuric acid having a concentration of about 20 percent by volume and being maintained at a temperature of between about 35 and 50C, and anodizing may be carried out at a current density of between 3 and 8 amperes per square centimeters.

EXAMPLE 3 The embodiment of the present example will be described with reference to FIG. 3 in which again certain ancillary devices corresponding to those of FIG. 1 have been omitted.

The essential difference between the embodiment of FIG. 3 as compared with that of FIG. 1 is that the etching is carried out in a direct current electrolytic cell 82, whereas anodizing is carried out in a two-chamber, alternating current electrolytic cell 48 which is substantially identical with cell 48 of FIG. 1.

According to the presently described example, strip 12 is fed from coil 10 over guide roller 86 which is connected to the negative terminal of the source of direct current and from there guided by guide rollers 92 through the electrolyte of the cell which consists of dilute hydrofluoric acid. The positive electrode 90, connected to the positive terminal of the source of direct current is immersed in the electrolyte.

The dilute hydrofluoric acid may have a concentration of 2 percent by volume and preferably will be maintained at about 45C. Etching is carried out at a current density of about 10 amperes per 100 square centimeters.

It will be understood from the description hereinabove that it is essential according to the present invention to carry out at least one of the two electrolytic processes, i,e., either the etching or the anodizing or both, in a cell of the type identified by reference numerals M and M, respectively. It becomes possible thereby to carry out the electrolytic etching and the electrolytic oxidation of aluminum or aluminum alloy foil, strip ll2 or the like in a sequential, continuous manner and thereby to realize substantial savings with respect to equipment, time and operating personnel. Furthermore, the actual treating periods according to the present invention are shorter than conventional treating periods and the quality of the foils or strips etched and anodized in accordance with the present invention compares favorably with the results obtained by conventional methods, particularly with respect to the uniformity and evenness of the toughening or etching of the strip. The control of the process is also greatly simplified.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of etching and anodizing devices differing from the types described above.

While the invention has been illustrated and described as embodied in a continuous electrolytic etching and anodizing apparatus for the treatment of aluminum and aluminum alloy foils, strips and the like, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spriit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent is:

11. An apparatus for sequentially etching and anodizing a sheet, foils and the like consisting essentially of aluminum or aluminum alloys in a continuous manner, said apparatus comprising electrolytic etching means for electrolytically etching such a sheet passing therethrough; electrolytic anodizing means for anodizing an etched sheet passing therethrough; a first source of electric current connected to said electrolytic etching means but not connected to said electrolytic anodizing means; a second of current connected to said electro lytic anodizing means but not connected to said electrolytic etching means; at least one of said means comprising two adjacent chambers for liquid electrolyte through which portions of said sheet are adapted to pass and a stationary electrode in each of said chambers, the source of electric current for said at least one of said means being a source of alternating current, connected to the stationary electrode in each chamber so that said current from said source will flow between said electrodes through said electrolyte and through said portions of said sheet in said chambers without passing through the sheet to the other of said means; and conveying means for continuously conveying said sheet first through said electrolytic etching means and thereafter through said electrolytic anodizing means.

2. An apparatus as defined in claim ll, wherein each of said means comprises two adjacent chambers for liquid electrolyte and a stationary electrode in each of said chambers, and wherein sources of alternating curll ili rent are connected to the stationary electrodes in the two chambers of each of said means, respectively.

3. An apparatus as defined in claim ll, wherein said electrolytic etching means comprises two adjacent chambers for an electrolyte consisting essentially of aqueous hydrochloric acid, and a stationary electrode, respectively, arranged in each of said two chambers, and means for connecting a first set of electrodes to a first source of alternating current; wherein said electrolytic anodizing means comprises two adjacent chambers for an electrolyte consisting essentially of aqueous sulfuric acid and each having a stationary electrode arranged for contact with the electrolyte of the respective chamber, and means for connecting a second set of electrodes to a second source of alternating current; and includes wet cleaning means for cleaning said sheet interposed between said electrolytic etching and anodizing means, said conveying means passing said sheet continuously in the indicated sequence, through said electrolytic etching means, said wet cleaning means and said electrolytic anodizing means.

4. An apparatus as defined in claim ll, and including rinsing means and sealing means arranged in the indicated sequence, downstream of said anodizing means for passing the anodized sheet therethrough so as to rinse and seal the oxide layer thereon.

5. An apparatus as defined in claim l and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for washing said sheet after etching and prior to anodizing the same, and wherein the external ohmic resistance between said sources of alternating current is such that no significant amount of current will flow externally therebetween.

b. An apparatus as defined in claim i, and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for washing said sheet after etching and prior to anodizing the same.

7. An apparatus as defined in claim 6, wherein said wet cleaning means include container means for holding an aqueous sodium hydroxide solution.

8. An apparatus as defined in claim 6 and including rinsing and drying means interposed in the indicated sequence between said cleaningmeans and said anodizing means.

9. An apparatus as defined in claim il, wherein said at least one of said electrolytic means is said electrolytic etching means, wherein said electrolytic anodizing means comprises a cell for an electrolyte consisting essentially of aqueous sulfuric acid, a stationary cathode, electrically conductive guide means interposed between said electrolytic etching means and said cell, for contacting and guiding said sheet toward said cell, wherein the source of current connected to said eiectrolytic anodizing means comprises a source of direct electric current, and including means for connecting said guide means and said cathode to said source of direct current, so that said sheet while passing through said cell will form the anode of said anodizing means, and including wet cleaning means interposed between said etching and anodizing means for passing said sheet therethrough so as to clean the same, said conveying means continuously passing said sheet, in the indicated sequence, through said electrolytic etching means, said wet cleaning means and said electrolytic anodizing means.

so that said sheet while passing through said cell will form the cathode of said etching means, and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for cleaning said sheet, said conveying means passing said sheet continuously and in said indicated sequence, through said electrolytic etching means, said wet cleaning means and said electrolytic anodizing means. 

2. An apparatus as defined in claim 1, wherein each of said means comprises two adjacent chambers for liquid electrolyte and a stationary electrode in each of said chambers, and wherein sources of alternating current are connected to the stationary electrodes in the two chambers of each of said means, respectively.
 3. An apparatus as defined in claim 1, wherein said electrolytic etching means comprises two adjacent chambers for an electrolyte consisting essentially of aqueous hydrochloric acid, and a stationary electrode, respectively, arranged in each of said two chambers, and means for connecting a first set of electrodes to a first source of alternating current; wherein said electrolytic anodizing means comprises two adjacent chambers for an electrolyte consisting essentially of aqueous sulfuric acid and each having a stationary electrode arranged for contact with the electrolyte of the respective chamber, and means for connecting a second set of electrodes to a second source of alternating current; and includes wet cleaning means for cleaning said sheet interposed between said electrolytic etching and anodizing means, said conveying means passing said sheet continuously in the indicated sequence, through said electrolytic etching means, said wet cleaning means and said electrolytic anodizing means.
 4. An apparatus as defined in claim 1, and including rinsing means and sealing means arranged in the indicated sequence, downstream of said anodizing means for passing the anodized sheet therethrough so as to rinse and seal the oxide layer thereon.
 5. An apparatus as defined in claim 1 and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for washing said sheet after etching and prior to anodizing the same, and wherein the external ohmic resistance between said sources of alternating current is such that no significant amount of current will flow externally therebetween.
 6. An apparatus as defined in claim 1, and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for washing said sheet after etching and prior to anodizing the same.
 7. An apparatus as defined in claim 6, wherein said wet cleaning means include container means for holding an aqueous sodium hydroxide solution.
 8. An apparatus as defined in claim 6 and including rinsing and drying means interposed in the indicated sequence between said cleaning means and said anodizing means.
 9. An apparatus as defined in claim 1, wherein said at least one of said electrolytic means is said electrolytic etching means, wherein said electrolytic anodizing means comprises a cell for an electrolyte consisting essentially of aqueous sulfuric acid, a stationary cathode, electrically conductive guide means interposed between said electrolytic etching means and said cell, for contacting and guiding said sheet toward said cell, wherein the source of current connected to said electrolytic anodizing means comprises a source of direct electric current, and including means for connecting said guide means and said cathode to said source of direct current, so that said sheet while passing through said cell will form the anode of said anodizing means, and including wet cleaning means interposed between said etching and anodizing means for passing said sheet therethrough so as to clean the same, said conveying means continuously passing said sheet, in the indicated sequence, through said elecTrolytic etching means, said wet cleaning means and said electrolytic anodizing means.
 10. An apparatus as defined in claim 1, wherein said at least one of said electrolytic means is said electrolytic anodizing means, wherein said electrolytic etching means comprises a cell for an electrolyte consisting essentially of aqueous hydrofluoric acid, a stationary anode and electrically conductive guide means for guiding said sheet into said cell and electrically connecting the same, wherein said source of current connected to said electrolytic etching means is a source of direct current, and means for connecting said guide means and said anode to said source of direct current so that said sheet while passing through said cell will form the cathode of said etching means, and including wet cleaning means interposed between said electrolytic etching means and said electrolytic anodizing means for cleaning said sheet, said conveying means passing said sheet continuously and in said indicated sequence, through said electrolytic etching means, said wet cleaning means and said electrolytic anodizing means. 